Television apparatus



K. SCHLESINGER 2,194,572

TELEVIS ION APPARATUS Filed March 18, 1937 2 Sheets-Sheet l MMW' March26, 1940. K. SCH LESINGER TELEVISION APPARATUS Filed March 18, 1937 2Sheets-Sheet 2 Patented Mar. 26 1940 UNlTED STATES ,194,572 TELEVISIONAPFARAT-US Kurt Schlesinger, Berlin, Germany, assignor, by

mesne assignments, to Loewe Radio, Inc, a corporation of New YorkApplication March 18,

1937, Serial No. 1131.688

In Germany March 21, 1936 3 Claims.

The present invention relates to relaxation circuits for televisionarrangements and represents an improvement for the known relaxationcircuit used for performing the deflection of the cathode ray in Brauntubes.

It is known to perform the deflection of the rayin cathode ray tubes bymeans of deflecting plates, simply bythe fact that the anode potentialsource of the tube charges'a relaxation condenser by way of a chargingresistance, and that the relaxation oscillation of the chargingcondenser produced by any desired discharge tubefor example ahot-cathode grid controlled glow discharge tube or controlledhigh-vacuum tube is generated in immediate fashion so as tobe of theorder of several hundred volts, 1. e., in such intensity that a specialamplifier for coupling between relaxation condenser and deflectingplates is no longer required. The known a1- rangementscertainly operateonly with earthed anode of the cathoderay tube. In a circuit of thisnature the control electrode of the tube is linked up negatively withhigh potential against earth. This causes difiiculties in the television25 modulation. Using an earthed cathode there arises the difficulty thatfor the purpose of withholding the anode potential a capacitativecoupling requires to be performed between the relaxation circuit and thedeflecting plates.

The invention will be clearly understood by way of example shown in theaccompanying drawings, in which I Fig. 1 shows the relaxation circuitgenerally used by means of which the foundations'of the presentinvention are explained.

Figs. 2, 3 and 4 show embodiments of the invention.

Fig. 1 explains the principle of such a circuit.

The anode battery i of the cathode ray tube, amounting to severalthousand volts, is earthed with its one pole, which is simultaneouslyconnected with cathode 2. The anode .3 is connected with the highpotential. l is the control grid, which is connected with areceiver E.The one deflecting plate 5 is connected with the anode. The otherdeflecting plate 5 must be coupled by way of a condenser i with therelaxationcircuit, and simultaneously it is connected with the anode byway of a leak resistance 8. The relaxation circuit consists of acharging condenser 9 and charging resistance it. For charging purposesthere is employed the anode potential I. The discharge may be performedin any known manner. In Fig. 1 there is shown a hot cathode gridcontrolled glow discharge tube H. In this circuit a resistance 12 isnecessary in any case, and the coupling. with the plates preferablytakes place, not at the condenser 9, but at the hot cathode gridcontrolled glow discharge tube H.

When using such a circuit the following dificulty occurs: The electroniccurrent passing to the deflecting plate s is already so considerable inpowerful, high-vacuum tubes of to-day that no more than approximately0.3 megohm can be used for theleak resistance 8. If on the other handthe condenser E is made so large that the relaxation curve for the slowimage change is transmitted without distortion, i. e., for example 0.5mf., the circuit 7/8 represents a load on the relaxation circuitamounting to 0.3 megohm. This load is already large as compared with thecharging resistance ill, or the charging resistance H3 would require tobe made still smaller than 0.3-megohmif the relaxation arrangement is tooperate in the idle condition. If, however, the charging resistance I0is chosen to approximately 0.1 megohm and the condenser 9, correspondingto the timeconstant, several microfarads, a much too powerful output isbrought, about in the relaxation circuit, and the hot cathode gridcontrolled glow dischargetube ii is very quickly overloaded upon thedischarge oi the large condenser. This represents one solution of theproblem being the foundation of an invention. In this case a timeconstant is given by the condition:

' R1o'CQE3-T and the alternating relaxation potential required at thecondenser, which potential may be ad- 5 justed at the grid bias 13 ofthe hot cathode grid controlled glow discharge tube. According to theinvention, R10 itself is made smaller than R8. Numerical example:

the potential at condenser 9=approx. 600 volts. The following output isbrought about:

According to the invention, the output in the 55 relaxation circuit isadjusted to be very much smaller than in accordance with the abovevalues.

The circuit then no longer operates in idle condition, but appears to bevery greatly loaded. The relaxation curve at the plate 6 is distortedaccordingly. The distortion appears in the form of a flattening effectin the direction towards the ignition point. According to the invention,the coupling between relaxation condenser and deflecting plate is madeto be dependent on the frequency viz., in such fashion that lowfrequencies are transmitted better than high frequencies. By this efiectthe said distortion underload is again eliminated.

Figs. 2 and 3 showv two possible embodiments of such an improvedcoupling. In Fig. 2 the anode battery l charges the condenser 9 byway ofresistance L The tube H discharges the condenser 9. The deflecting plate5 is coupled with the tapping of the resistance It] by way of theblocking condenser 7 which is proof against high tension, and with theanode by means of the leak resistance 8. The tapping at the resistanceill is so adjusted that the part of. this resistance, which is connectedto the plate 6, is greater than the reactance of the condenser Q inrespect of the lowest relaxation frequency, i. e., the number ofrelaxations per second. By fine variation of the resistance It] anadjustment is to be found at which an undistorted relaxation curveappears on the screen. Numerical example:

. 9:0.02 mf., Relaxation frequency :25 periods,

:3- 10 ohms,

8:0.3- 10 ohms A disadvantage of the method according to Fig. 2 is aloss of size caused by the potential distribution 10/8. Thisdisadvantage is exhibited to smaller extent by the corrected couplingaccording to Fig. 3.

In Fig. 3 the relaxation condenser 9 is charged in the usual manner byway of the charging resistance Hi and discharged byway of the hotcathode grid controlled glow discharge tube H and resistance I2.Coupling is also effected in usual manner by way of a blocking condenseri in direct fashion with the anode of the glow discharge tube H. vThecoupling, however,in 'accordance with the invention is performed via ahigh-frequency filter /16 before it is connected with the deflectingplate 6. By means of the filter 15/16 there is evidently caused, exactlyin the same manner shown in Fig, 2, a weakening of the higher relaxationharmonics and there oc-- curs a correction of the distortions arisingfrom the load. The amplitude .efiiciency is somewhat better than in Fig.2, as the load is reduced by the filtering series resistance l5.Dimensions:

15:02-10 ohm s, 16=approximately 0.2 mf.,

8:0.3-10 ohms,

The idea might be conceived of negatively biassing the two plates 5 and5 in common in relation to the anode 3. This, however, would lead to badsharpness of the image points and decrease in the output of the ray bybraking action. Accordingto the invention, the two plates 5 and 6, inaccordance with Fig. 4, are disposed behind a screening means 17/18ofspecial form. This screening means is directly connected with theanode 3 or is weakly positively biassed in relation thereto. It consistsof very thin wires, which are disposed in the longitudinal direction, i.e., parallel to the ray. There may also be employed wire nets. Thereciprocal of the plates 5 and B through these wires should be made aslarge as possible. The plates 5 and 6 are now linked up directly or byWay of the leak resist ance 8 with a bias which is negative in relationto the anode potential. This bias may be derived at a tapping iii of theanode-battery i. The bias 39, negative in relation to the anode, is madeto be equal to or greater than the highest positive oscillation peak ofthe deflecting potential at 6. Subject to absence of current the leakresistance a may be made of the order of It) to 20 megohms. The slowestrelaxation frequency may then be transmitted with a correspondinglysmall condenser of approximately 1,000 cm., and the relaxation apparatusmay be allowed to operate with very small output, the chargingresistance it! having several megohms, the charging condenser i! beingcomparatively small (0.02 mi.) and the charging output being equal to C9e9 i. e., proportional to C, so that it accordingly remains small.

I claim:

1. In a television apparatus comprising a cathode ray tube, having acathode, an anode and at least one pair of deflecting plates, arelaxation oscillator for generating a linear saw tooth voltagedeflecting the cathode ray in said cathode ray tube. and a source ofhigh direct voltage, said anode of the cathode ray tube being connectedto said high voltage source, at least one of said deflecting platesbeing for a time more positive than the cathode ray effecting a currentin the deflecting circuit. and means to prevent distortions of thedeflecting curve of said cathode ray caused by said current in thedeflecting circuit loading said relaxation generator.

2. In a television apparatus comprising a cathode ray tube, having acathode, an anode and at least one pair of deflecting plates, atrelaxation oscillator for generating a linear saw tooth voltagedeflecting the cathode ray in said cathode ray tube, and a source ofhigh direct voltage, said anode of the cathode ray tube being connectedto said high voltage source, the positive terminal of which beingconnected directly to the anode of said cathode ray tube, to one of saiddeflecting plates and to the input of said relaxation oscillator, theother deflecting plate being connected via a leak resistance to theanode of said cathode ray tube and via a condenser to the output of saidrelaxation generator, at least one of said deflecting plates being for atime more positive than the cathode ray effecting a current in thedeflecting circuit, and means to prevent distortions of the deflectingcurve of said cathode ray caused by said current in the deflecting air--cult loading said relaxation generator.

In a television apparatus comprising a cathode ray tube, having acathode. an anode and at least one pair of deflecting plates, arelaxation oscillator for generating a linear saw tooth voltagedeflecting the cathode ray in said cathode ray tube, and a source ofhigh direct voltage, said anode of the cathode ray tube being connectedto said high voltage source, at least one 5 of said deflecting platesbeing for a time more positive than the cathode ray eifecting acurrentin the deflecting circuit, and coupling means between said relaxationoscillator and said deflecting circuit favouring the lower frequenciesin order to prevent distortions of the deflecting curve of said cathoderay caused by said current in the deflecting circuit loading saidrelaxation 5,

generator.

KURT SCI-ILESINGER.

